Assessment of peripheral artery tonometry in the detection of treadmill exercise-induced myocardial ischemia

Peripheral arterial tonometry-PAT technology

PAT Technology is a plethysmographic based measurement method which facilitates the accurate recording of the pulsatile volume changes of the arteries of peripheral vascular beds at the distal end of the fingers over sustained periods of time. It represents a departure from previously available plethysmographic methods, in so far as it applies a uniform pressure field which completely envelopes the measured part of a digit, including its distal-most tip. Applying near diastolic blood pressure levels of pressure within the PAT probe optimizes the dynamic range of the signal, prevents confounding veno-arteriolar reflex vasoconstriction at the measurement site, reduces respiratory and movement artifacts and thus facilitates accurate long term measurement. The vascular bed of the distal phalanx of the finger is a major site of sympathetic nervous system mediated vasoconstrictor activity, and the PAT response to sympathetic changes provides a platform for accurate and robust measurement in a number of sleep and sleep related clinical areas, foremost as a patient friendly and extensively validated home sleep testing device.

Peripheral microcirculatory hemodynamic changes in patients with myocardial ischemia

BACKGROUND

Patients with coronary heart disease demonstrate changes in skin microcirculation and a decrease in cutaneous blood mass.

OBJECTIVE

The goal of this study was to assess the feasibility of diagnosing myocardial ischemia based on peripheral microcirculatory variables.

METHODS

The skin microcirculatory measurements were monitored using an LPT system comprising a Laser Doppler Flowmeter (LDF), a photoplethysmograph (PPG) and a transcutaneous oxygen tension device (tc-PO2). Concurrently, heart rate and blood pressure were monitored. Measurements were performed before and after exercise stress test. Subjects were divided into ischemic (20) and nonischemic (27) patients based on myocardial perfusion imaging (MPI).

RESULTS

The results indicate differences in LPT variables between ischemic and nonischemic patients following exercise, while no differences in the central variable values were observed between the two groups.

CONCLUSIONS

Peripheral microcirculatory variables may be useful for non-invasive assessment of myocardial ischemia. The system has clinical potential for sensitive and noninvasive monitoring of vital variables during medical procedures in clinics, as well as in home care for patients who suffer from ischemic cardiac diseases.

Exercise-induced vasodilation in healthy males: A marker of reduced endothelial function

OBJECTIVES

Reduced arterial vasodilatatory capacity is a marker of coronary heart disease. The aim was to investigate if the difference between the vasodilatory response before and after exercise, as assessed by non-invasive methodology, is related to endothelial and inflammatory biomarkers.

DESIGN

Post-ischemic hyperemia after 5 min of arterial occlusion was examined before and after a bicycle test with strain-gauge plethysmography (measuring peak reactive hyperemia in the forearm) and peripheral arterial tonometry (PAT hyperemia ratio: measuring pulse waves in the index finger relative to the contra-lateral index finger) in 30 healthy males. A low PAT hyperemia ratio or a low peak reactive hyperemia reflects endothelial dysfunction. Inflammatory and endothelial biomarkers were assessed.

RESULTS

A low peak reactive hyperemia and a low PAT hyperemia ratio before the bicycle test was associated with a high percentage increase in peak reactive hyperemia after exercise (r = - 0.68, p < 0.001; r = - 0.35, p = 0.06, respectively). Asymmetric dimethylarginine and interleukin-10 were associated with the percentage increase in peak reactive hyperemia in multiple linear regression analyses (β: 165 (confidence interval [CI], 34-296), p = 0.02; β: 19 (CI, - 0.5-39), p = 0.06, respectively).

CONCLUSIONS

The difference in the vasodilatory response before and after exercise, as assessed by non-invasive methodology, is related to endothelial and inflammatory biomarkers in healthy males.

Evaluation of endothelial function by peripheral arterial tonometry and relation with the nitric oxide pathway

Endothelial dysfunction is an important component in the development of cardiovascular diseases. Endothelial function may be evaluated by peripheral arterial tonometry (PAT) which measures the vasodilator function in the microvasculature of the fingertip during reactive hyperaemia. The reactive hyperaemia index (RHI) is decreased in the presence of cardiovascular risk factors and thus far several studies have shown that PAT-RHI may provide reliable prediction of outcome. The technique is operator independent and easy to perform. Abnormalities measured by PAT follow the same trend as those measured by flow-mediated dilation in the brachial artery, but the two methods are not interchangeable. We have reviewed the recent literature in an effort to evaluate peripheral arterial tonometry as a method to assess the function of the endothelium and additionally suggest directions for future research. Special attention will be directed to the nitric oxide dependency of the reactive hyperaemia index obtained by peripheral arterial tonometry.

Low-carbohydrate, high-protein, high-fat diet alters small peripheral artery reactivity in metabolic syndrome patients

BACKGROUND

Low carbohydrate diets have become increasingly popular for weight loss. Although they may improve some metabolic markers, particularly in type 2 diabetes mellitus (T2D) or metabolic syndrome (MS), their net effect on vascular function remains unclear.

OBJECTIVE

Evaluate the relation between dietary macronutrient composition and the small artery reactive hyperaemia index (saRHI), a marker of small artery vascular function, in a cohort of MS patients.

DESIGN

This cross-sectional study included 160 MS patients. Diet was evaluated by a 3-day food-intake register and reduced to a novel low-carbohydrate diet score (LCDS). Physical examination, demographic, biochemical and anthropometry parameters were recorded, and saRHI was measured in each patient.

RESULTS

Individuals in the lowest LCDS quartile (Q1; 45% carbohydrate, 19% protein, 31% fat) had higher saRHI values than those in the top quartile (Q4; 30% carbohydrate, 25% protein, 43% fat) (1.84±0.42 vs. 1.55±0.25, P=.012). These results were similar in T2D patients (Q1=1.779±0.311 vs. Q4=1.618±0.352, P=.011) and also in all of the MS components, except for low HDLc. Multivariate analysis demonstrated that individuals in the highest LCDS quartile, that is, consuming less carbohydrates, had a significantly negative coefficient of saRHI which was independent of confounders (HR: -0.747; 95%CI: 0.201, 0.882; P=.029).

CONCLUSIONS

These data suggest that a dietary pattern characterized by a low amount of carbohydrate, but reciprocally higher amounts of fat and protein, is associated with poorer vascular reactivity in patients with MS and T2D.

Negative effect of a low-carbohydrate, high-protein, high-fat diet on small peripheral artery reactivity in patients with increased cardiovascular risk

Low-carbohydrate diets have become increasingly popular for weight loss. Although they may improve some metabolic markers, particularly in type 2 diabetes mellitus (T2D) or the metabolic syndrome (MS), their net effect on arterial wall function remains unclear. The objective was to evaluate the relation between dietary macronutrient composition and the small artery reactive hyperaemia index (saRHI), a marker of small artery endothelial function, in a cohort of patients at increased cardiovascular (CV) risk. The present cross-sectional study included 247 patients. Diet was evaluated by a 3-d food-intake register and reduced to a novel low-carbohydrate diet score (LCDS). Physical examination, demographic, biochemical and anthropometry parameters were recorded, and the saRHI was measured in each patient. Individuals in the lowest LCDS quartile (Q1, 45 % carbohydrate; 20 % protein; 32 % fat) had higher saRHI values than those in the top quartile (Q4, 29 % carbohydrate, 24 % protein, 40 % fat; 1·66 (sd 0·41) v. 1·52 (sd 0·22), P= 0·037). These results were particularly strong in patients with the MS (Q1 = 1·82 (sd 0·32) v. Q4 = 1·61 (sd 027); P= 0·021) and T2D (Q1 = 1·78 (sd 0·31) v. Q4 = 1·62 (sd 0·35); P= 0·011). Multivariate analysis demonstrated that individuals in the highest LCDS quartile had a significantly negative coefficient of saRHI, which was independent of confounders (OR − 0·85; 95 % CI 0·19, 0·92; P= 0·031). These findings suggest that a dietary pattern characterised by a low amount of carbohydrate, but high amounts of protein and fat, is associated with a poorer small artery vascular reactivity in patients with increased CV risk.

Effects of therapeutic lifestyle changes on peripheral artery tonometry in patients with abdominal obesity

BACKGROUND AND AIMS

Abdominal obesity (AO) is associated with endothelial function (EF) alteration and increased global cardiovascular (CV) risk. Therapeutic lifestyle changes (TLSC) reduce CV risk, but the impact on EF assessed by peripheral artery tonometry (PAT) is unknown. In this study, we aimed to prospectively assess the effects of TLSC on EF measured by PAT in increased CV risk patients with AO.

METHODS AND RESULTS

150 patients with AO and moderate CV risk were randomized to groups receiving a one-year intervention of either conventional medical care (control group, CG) or an intensive TLSC program (intervention group, IG). Vascular studies (EF by PAT, intima-media thickness (IMT)) and lifestyle (LS) assessment were performed before and after intervention. The PAT ratio improved in the IG and worsened in the CG. The global CV risk was reduced (P = 0.017) in the IG due to a significant decrease in systolic blood pressure (P < 0.001), increase in HDL cholesterol and ApolipoproteinA1 (P = 0.013). More individuals in the IG than in the CG quit smoking (P = 0.001) and increased their physical activity (P = 0.014). The improvement in at least two LS components was associated with a PAT ratio increase (2.44 IC: 95% 0.99-6.00, P = 0.051). The PAT ratio increase determined less IMT progression (-1.1 IC: 95% 0.91-1.00, P = 0.053).

CONCLUSIONS

Good adherence to a TLSC program reduces global CV risk and determines PAT ratio improvement. The PAT ratio increase is the main determinant of lower IMT progression.

Assessment of vascular endothelial function with peripheral arterial tonometry: information at your fingertips?

Endothelial dysfunction is an important component in the pathogenesis of atherosclerosis. The ability to assess the endothelium in a meaningful manner has been the subject of intense investigation over decades. Since the function of endothelial cells is a gauge of vascular health, assessment of vascular function is emerging as a useful tool for predicting cardiovascular risk and as a surrogate outcome measure for cardiovascular reduction intervention studies. This review highlights techniques for assessing endothelial function, focusing on a novel method of determining peripheral vascular reactivity via arterial tonometry.

Usefulness of peripheral arterial tonometry in the detection of mental stress-induced myocardial ischemia

BACKGROUND

Mental stress-induced myocardial ischemia (MSIMI) identifies a subset of coronary arterial disease (CAD) patients at increased risk for adverse cardiovascular events. Peripheral arterial vasoconstriction has been consistently reported as an underlying mechanism for ischemia development in this setting and as such affords a unique opportunity for the noninvasive detection of this phenomenon.

HYPOTHESIS

We studied the usefulness of a peripheral arterial tonometry (PAT) technique in the detection of MSIMI. We sought to identify response patterns that would predict the development of MSIMI.

METHODS

Participants were 211 patients with documented CAD. Mental stress testing was performed using a public speaking task. Rest-stress myocardial perfusion imaging was the gold standard for ischemia detection. PAT responses were assessed during the 2 phases of the stressful task (stress anticipation and the task performance) and were calculated as a ratio of stress to the resting pulse wave amplitude.

RESULTS

Vascular response during the stress anticipation period (speech preparation) was more pronounced than during the actual speaking task (the mean preparation index was 0.64 +/- 0.53; the mean speech index was 0.72 +/- 0.60; P < 0.001). PAT response during speech preparation had modest accuracy for predicting MSIMI (area under the curve [AUC] was 0.63; 95% confidence interval [CI]: 0.53-0.74, P = 0.015). A PAT index < or = 0.52 was identified as the best cut off value for detecting MSIMI with a sensitivity of 76% and a specificity of 56%.

CONCLUSION

We identified a pattern of peripheral arterial response to mental stress that has a relatively modest accuracy in predicting MSIMI. Further research is needed to validate the findings of this study.

Nocturnal pulse wave attenuation is associated with office blood pressure in a population based cohort

OBJECTIVE AND BACKGROUND

Pulse wave amplitude (PWA) derived from the digital vascular bed has been used in sleep studies. The nocturnal attenuation of PWA has been shown to reflect sympathetic activation during sleep. We assessed the relationship between nocturnal PWA attenuation and office blood pressure (BP).

METHODS

Eighty-one subjects (46 men; age 60+/-7 years; body mass index [BMI] 28.2+/-4.3 kg/m(2); apnea hypopnea index [AHI], 25.4+/-22.6 events/h; systolic BP 137+/-15 mm Hg; diastolic BP 79+/-7 mm Hg) recruited from a population based cohort underwent simultaneous ambulatory polysomnography (PSG) and peripheral arterial tonometry (PAT) recording. Episodic attenuations of PWA derived from the pulse waveform of the PAT signal were identified and characterized. Generalized least squares regression models were used to identify the associations between median PWA attenuation (PWA.att), office BP and sleep-related disordered breathing.

RESULTS

We found that the association between PWA.att and office BP was independent of gender, age, BMI, antihypertensive medication, number of attenuation episodes, AHI, oxygen desaturation 4% index (ODI4) and arousal index. Each 10% increase in PWA.att was associated with increases of 5.0 mm Hg systolic BP (P=0.02) and 3.0 mm Hg diastolic BP (P=0.005). We also found independent relationships between systolic/diastolic BP and BMI (P=0.0006/0.001), AHI (P=0.03/0.1) and ODI4 (P=0.03/0.03).

CONCLUSIONS

The degree of PWA attenuation during the night is associated with office BP independent of sleep-disordered breathing. Continuous assessment of PWA during sleep may provide novel insights into cardiovascular physiology and morbidity.

Noninvasive detection of risk for emotion-provoked myocardial ischemia

OBJECTIVES

To test an easily administered, noninvasive technology to identify vulnerability to mental stress ischemia.

BACKGROUND

Myocardial ischemia provoked by emotional stress (MSI) in patients with stable coronary artery disease (CAD) predicts major adverse cardiac events. A clinically useful tool to risk stratify patients on this factor is not available.

METHODS

Patients with documented CAD (n = 68) underwent single photon emission CT myocardial perfusion imaging concurrent with pulse wave amplitude assessment by peripheral arterial tonometry (PAT) during a mental stress protocol of sequential rest and anger stress periods. Heart rate and blood pressure were assessed, and blood was drawn for catecholamine assay, during rest and stress. MSI was defined by the presence of a new perfusion defect during anger stress (n = 26) and the ratio of stress to rest PAT response was calculated.

RESULTS

Patients with MSI had a significantly lower PAT ratio than those without MSI (0.76 +/- 0.04 versus 0.91 +/- 0.05, p = .03). An ROC curve for optimum sensitivity/specificity of PAT ratio as an index of MSI produced a sensitivity of 0.62 and a specificity of 0.63. Among patients taking angiotensin converting enzyme (ACE) inhibitors, the sensitivity and specificity of the test increased to 0.86 and 0.73, respectively; 90% of patients without MSI were correctly identified.

CONCLUSIONS

PAT in concert with ACE inhibition may provide a useful approach to assess risk for MSI. Future studies should help determine how best to utilize this approach for risk assessment in the clinical setting.

Noninvasive detection of the hemodynamic stress of exercise using the photoplethysmogram

Exercise induced hemodynamic stress has been studied extensively using a wide range of physiological sensors. While athletes can modulate their training intensity using EKG-based heart rate monitors, there are currently no noninvasive monitors that can be used to ascertain with a high degree of certainty the hemodynamic stress an individual is experiencing because of fatigue or an underlying pathology. We propose that cardiac stress will result in detectable changes in skin blood flow. In a clinical trial with eleven healthy subjects performing the Bruce Protocol treadmill test low frequency waves were observed in the blood flow to both the forehead and ear, but not the finger, using photople- thysmographs (PPG) measured by a pulse oximeter. As volitional fatigue approached, the low frequency (f = 0.05-0.2 Hz) amplitude modulation observed in the PPG became more pronounced; then, within several seconds of the cessa- tion of the protocol, they disappeared. Using a software-based detector, these distinct waves are reliably detected, with a low incidence of false positives, in all subjects before the onset of volitional fatigue. We hypothesize that the low frequency waves observed in the PPG of individuals exercising to volitional fatigue provide a mechanism for noninvasively detecting hemodynamic stress to the human vascular system.

Detection of chest pain of non-cardiac origin at the emergency room by a new non-invasive device avoiding unnecessary admission to hospital

Recent advances in the treatment of acute coronary syndromes has raised awareness that prompt presentation for chest pain may be life saving. Most patients presenting with chest discomfort have a non-ischaemic ECG on presentation, but are routinely admitted to hospital because of diagnostic uncertainty for occult MI or ischaemia. We tested a new non-invasive device that measures central aortic pressure changes (dP/dtejc): an accepted index of myocardial performance that could be added to the diagnostic triage of ischaemia in the ER avoiding unnecessary admissions. We followed 85 patients presenting at the ER with acute chest pain. In 72 patients, negative ECG and myocardial enzyme dynamics ruled out coronary origin during the first 24 h after admission. In 8 of the 72 patients, coronary catheterisation found normal coronary arteries. In this group, average dP/dtejc was 163 (range 92-232). In 35 patients in whom the new non-invasive cardiac performance index dP/dtejc was above a threshold of >150, acute MI was ruled out. In 13 patients, acute chest pain had coronary origin confirmed by ECG and/or positive enzymes. The average dP/dtejc in this group was 117 (range 61-149). The dP/dtejc values were found to be significantly higher in patients without acute MI (p<0.001). Preliminary findings suggest that nearly 40% of patients presenting with acute chest pain could be spared the risks and costs of unnecessary hospital admission and more invasive cardiac testing by simply adding a easy to use, immediately obtained, test to the diagnostic protocol, and using a threshold of dP/dtejc>150 to rule out heart attack.